The present invention has as its subject pigment pastes which comprise as binder at least one polyurethane acrylate (P) that is obtainable by polymerizing, in an organic solvent or in a mixture of organic solvents,
(A) ethylenically unsaturated monomers, or a mixture of ethylenically unsaturated monomers, in the presence of
(B) a polyurethane resin which has a number-average molecular weight of from 200 to 30,000, preferably from 1000 to 5000, and which contains on average from 0.05 to 1.1, preferably from 0.2 to 0.9 and, with particular preference, from 0.3 to 0.7 polymerizable double bonds per molecule, and converting the resulting reaction product into an aqueous dispersion.
The present invention also relates to aqueous coating materials comprising these pigment pastes and to methods of coating substrates. Finally, the invention relates as well to mixer systems using these pigment pastes.
Aqueous coating materials are pigmented by adding aqueous pigment concentrates, so-called pigment pastes, to the other constituents of the coating material.
Pigment pastes consist usually of water, at least one pigment, at least one water-dilutable binder and, if desired, organic solvents, wetting agents and other additives customary for pigment pastes (cf. Volker Radke in xe2x80x9cPigmente fxc3xcr Anstrichmittelxe2x80x9d [Pigments for coating materials], Technische Akademie Esslingen, Kap. 7, Dispersion of Pigments, Export-Verlag, 1990).
In order for these pigment pastes to be able to be used as universally as possible and so permit the cost-effective preparation of a large number of in some cases very different paints, these pigment pastes should be as highly pigmented as possible. However, this leads in turn generally to a large number of problems, such as high pigment paste viscosity, inadequate pigment paste shelf life (in general, the pigment pastes are desired to have a shelf life of at least 6 months on storage at room temperature or one month on storage at 40xc2x0 C.) or poor dispersibility (in other words, a high specific energy input is necessary for dispersing, or the pigment paste thickens in the course of the dispersing operation, or there is a tendency to settling after treatment with a dissolver).
EP-B-521 928 discloses polyurethane acrylates (P) of the type specified at the outset, and their use for preparing pigment pastes. EP-B-521 928, however, merely describes the preparation of three different basecoats using two different white pastes and one pigment paste containing carbon black. Other pigment pastes are not described in EP-B-521 928.
In addition, EP-B-297 576 discloses aqueous polyurethane resin dispersions which are obtainable by polymerizing ethylenically unsaturated compounds in water in the presence of a polyurethane resin which has no double bonds. These polyurethane resin dispersions can likewise be employed, alone or together with other grinding resins, for grinding pigments in order to prepare aqueous coating materials. In EP-B-297 576, however, it is preferred not to employ, as paste resins, hydroxyl-containing acrylate copolymers prepared in the presence of polyurethanes. Furthermore, the preparation of universal pigment paints is not described in EP-B-297 576.
EP-B-438 090, furthermore, discloses pigment pastes and their use in aqueous coating materials, these pigment pastes comprising a polyester urethane as grinding binder. The use of urethane acrylates as grinding binders, in contrast, is not described in EP-B-438 090. These pigment pastes known from EP-B-438 090 have the disadvantage that the stability of highly pigmented pastes, in respect of viscosity, colour strength and stability of shade in the course of storage of the pigment pastes, is in need of improvement.
In comparison to the pastes known from this EP-B-438 090, the pigment pastes of the present application, despite their high pigment content, are intended to be virtually stable in viscosity on storage of the pastes at room temperature for 6 months; in other words, the viscosity of the pastes after storage remains in the range between 50 and 1000 mPa.s under a shear stress of 1000 sxe2x88x921. In addition, the pigment pastes of the present invention should despite the high pigment content remain stable in terms of colour strength and shade (xc2x110%, xcex94Exe2x89xa61.5) on storage of the pastes at room temperature for 6 months.
EP-A-424 705, furthermore, discloses pigment pastes which as grinding binders of a nonionically or partly anionically stabilized dispersion comprise an acrylate/polyurethane graft copolymer. These pigment pastes known from EP-A-424 705 differ from the pigment pastes of the present Application in that the pigment pastes described therein have a low pigment/binder ratio and require long milling periods and/or a high specific energy input ( greater than 1000 Wh/kg).
Finally, EP-A-311 209 discloses universal pigment pastes and their use in mixer systems for preparing aqueous and conventional paints. The pigment pastes described therein and used to prepare aqueous paints comprise from 0 to 65% by weight of binder, from 10 to 65% by weight of pigment and also organic solvents and, if desired, further additives. Binders specified for the pigment pastes in EP-A-311 209 are alkyd resins and polyurethane resins. The use of urethane acrylates, on the other hand, is not specified in EP-A-311 209. The pigment pastes in EP-A-311 209 have the disadvantage of a high volatile organic content (VOC).
The object on which the present invention is based, therefore, is to provide aqueous pigment pastes which are universally employable and which are easy and cost-effective to prepare. In addition, these pigment pastes should meet the usual requirements. They should therefore in particular have a high level of pigmentation and at the same time an adequate shelf life (at least 6 months on storage at room temperature or 1 month on storage at 40xc2x0 C.), good dispersibility (i.e. e.g. required specific energy input 50-1000 Wh/kg) and good processability (e.g. pumpability). The pigment pastes should, furthermore, show good formulation and colouristic properties. Finally, the pigment pastes should possess a high colouristic saturation, good colour strength, or good hiding power, and good flow properties.
This object is surprisingly achieved by pigment pastes of the type specified at the outset which are characterized in that they comprise
(Pa) from 10 to 35% by weight of at least one polyurethane acrylate resin (P), based on the solids content,
(Pb) from 10 to 65% by weight of water and
(Pc1) from 18 to 40% by weight of at least one organic, transparent pigment or from 30 to 50% by weight of at least one organic, opaque pigment, or
(Pc2) from 30 to 80% by weight of at least one inorganic pigment, with the exception of white pigments, or from more than 50 to 70% by weight of white pigment, or
(Pc3) from more than 8 to 15% by weight of carbon black,
the proportions by weight of the respective components (Pa) to (Pc) being based in each case on the overall weight of the pigment paste.
Further subjects for the present invention are aqueous paints comprising these pigment pastes, and methods of coating substrates using these paints. Finally, the invention also relates to mixer systems based on these pigment pastes.
It is surprising and was not foreseeable that using the polyurethane acrylates (P) it would be possible to prepare very highly pigmented and yet storage-stable, readily processable pigment pastes which meet the common requirements relating to pigment pastes. Thus it was not foreseeable that it would even be possible in general to operate with a level of pigmentation in the vicinity of the critical pigment volume concentration (c.p.v.c.). Preferably, the level of pigmentation in this context is generally from about 30 to 10%, with particular preference from 5 to 7%, below the c.p.v.c.
Surprisingly, despite the high pigment content, the pigment pastes of the invention even after storage are both virtually stable in viscosity (in other words, the viscosity even after storage at room temperature for 6 months remains at from 50 to 1000 mPa.s at a shear rate of 1000 sxe2x88x921) and stable in terms of the colour strength and in terms of the shade (i.e. colour strengthxc2x110%, xcex94Exe2x89xa61.5).
A further advantage, finally, is that despite the high pigmentation no dispersing problems arise. For example, an energy input of just 50-1000 Wh/kg, preferably 100-400 Wh/kg, is generally sufficient for dispersion. In addition there are generally no problems, for example, such as thickening during the grinding operation or settling after treatment in a dissolver.
In the text below the individual constituents of the pigment paste of the invention will first of all be elucidated further.
The polyurethane acrylates (P) employed as binders in the pigment pastes of the invention are known and are described, for example, in EP-B-521 928 on page 2, line 56 to page 8, line 16. For details regarding the preparation of these polyurethane acrylates reference is therefore made to this description in EP-B-521 928.